Chassis

Tire Pressure Monitoring (2nd generation)

Timely detection of a gradual loss of pressure not only increases driving safety, but can also prevent uneven tire wear and high fuel consumption. The optional Tire Pressure Monitoring system (TPM) has therefore been available for all Cayenne models since 2003. It continually monitors the air pressure in all four tires and displays this information for the driver in the instrument cluster.

The new Tire Pressure Monitoring system (TPM) generation is standard equipment for all Cayenne models in the North American market. The most important additional function in the system is the option for automatically and quickly detecting the wheels mounted on the vehicle (own wheels) and their installation position.

The radio signals from the wheel electronics units are requested by the control unit as required via the trigger senders. The system detects the vehicle's own wheels and the installation position of own wheels by evaluating the trigger location and performing a statistical evaluation of the wheel electronics information received.

Component Locations

The system comprises the following components.







Control Unit

As in previous models, the control unit is located above the mounting saddle for the foot operated parking brake in the driver's footwell. The control unit analyses the incoming data from the antenna and forwards the relevant information to the instrument cluster. Since the data is transmitted via cable from the central antenna, the control unit is designed to pick up both frequencies (433 RoW/315 MHz USA/Canada). If a new control unit is installed, it must be coded accordingly.

Input signals via CAN

- Vehicle speed
- Outside temperature
- Engine speed

Input signals via LIN (Local Interconnect Network)

- Four wheel electronics units via the digital central antenna

Output signals

- Front left trigger
- Front right trigger
- Rear right trigger
- Rear left trigger
- Instrument cluster

Triggers (trigger senders)







The four triggers, which are located under the wheel housing liners in each of the four wheel housings, send a 125 kHz signal directly to the wheel electronics units in order to transmit the desired information to a central antenna immediately.

When the vehicle is unlocked, the control unit initiates the first 125 kHz signal for each trigger in the four wheel housings one after the other, starting at the left front in clockwise direction. Then, the wheel electronics units are only triggered approx. every 60 seconds while the vehicle is moving. Since the range of the trigger coils is limited to the relevant wheel housing, any possibility of interference affecting other wheels is almost totally eliminated. Depending on many and varied influences from the immediate environment, such as reflections (wet roads, metal grates, guide rails, etc.), external interference (external transmitters), a trigger signal can fail to reach the related wheel sensor or the feedback data protocol can get lost on its way to the central antenna.

The control unit responds immediately by re-triggering the trigger - repeatedly if necessary at the wheel position at which the expected protocol had failed to materialize as soon as the initiated trigger cycle from front left to rear right is completed. This concept reduces system interference and the wheel electronics units are detected much faster.

Central Antenna







NOTE: The central antenna is designed to pick up various frequencies (433 RoW/315 MHz USA/Canada).

The digital central antenna (reception frequency 315) is secured close to the center of the underside of the left side member under the vehicle and is protected from stone damage by the sill cover. The signals received from the wheel electronics units are digitalized in the antenna and forwarded to the control unit via two normal lines (LIN bus). The digital antenna has an integrated self-diagnosis facility. This means that when a fault is detected, it is stored in the control unit fault memory and displayed on the PIWIS Tester.

Wheel Electronics

The wheel electronics unit (wheel transmitter 315 MHz) is screwed to the rim using the wheel valve.

The wheel electronics unit comprises the following components:
- Pressure sensor,
- temperature sensor,
- roll switch,
- measuring and control electronics,
- receiver and transmitter,
- and a battery.

The wheel electronics unit can be triggered and receives send requests from the TPM control unit via four triggers. This means that the antenna always receives only one data protocol and this comes from the wheel electronics unit that received the request to send. This gives the system added protection against interference affecting other antennas. Higher transmission power is used due to the longer radio link to the central antenna.

The roll switch detects whether the wheel is stationary or turning. This information is used either to start a triggered learning process for a moving wheel or to switch off the wheel electronics unit when the wheel has been stationary for a long time.

To avoid confusion with 1st generation wheel electronics, the new wheel electronics unit can be identified by the modified shape of the housing and the small air filter. A modified data protocol ensures that the wheel electronics unit will not be detected if incorrect part is installed and this is stored as a fault in the fault memory.







The following aspects of the system have been optimized by changing the system hardware and software:

Fast learning following a wheel change. The wheels of a newly mounted set of wheels are assigned within one minute - often even within a few seconds of selecting the set of wheels in the "Tire pressure" menu and the pressure values are displayed.

Fast Detection of a Wheel Change Without Re-Calibration

If the TPM system is not re-calibrated following a wheel change, the system detects this within max. 3 minutes of driving the vehicle and generates the message "Wheel change? Make new selection" in order to ensure that the correct nominal pressure is configured for the monitoring process by selecting the correct tires.

Immediate Pressure Display at the Start of Each Trip

The TPM control unit knows which wheel set is mounted on the vehicle once the teaching process is complete. The tire pressure values are available as soon as the vehicle is started since the trigger cycle starts immediately once the door is opened and the wheel electronics units have sent the latest data to the control unit.

Fast Pressure Update Following Tire Pressure Adjustment

The differential pressure display filling information in the "Tire pressure" menu is still available when the vehicle is stationary in order to ensure that the tires are filled correctly. As soon as this information is called up, a fast pressure update is generated over a time span of max. 15 minutes and this update information shows the current tire pressure every 10 seconds during tire pressure adjustment.

Partial Monitoring







If a spare wheel without a wheel sensor is mounted in the event of a flat wheel, a unique allocation of the remaining wheel electronics units can still be detected by the trigger system. In this case, the system remains active both when an emergency spare wheel or a spare wheel with no wheel sensor is used, as well as if one or two sensors fail (e.g. due to sealant) and continues to monitor the wheels using the wheel electronics units that are still active.

NOTE: If a spare wheel with a wheel sensor is mounted in the event of a flat wheel and if this is confirmed by selecting "Spare wheel" is the Spare wheel menu, this wheel will be incorporated into the monitoring process following a brief learning phase.

System Cannot be Switched Off, Warning can be Acknowledged

The TPM system can no longer be switched off. As a result, if the pressure is deliberately reduced well below the nominal pressure, e.g. for improved traction on extremely soft or sandy terrain, a flat wheel message will appear continuously in the display.

The hard (red) warning can be acknowledged with the new TPM generation. This clears the display so that any other messages and/or information can be shown. The TPM light in the instrument panel remains activated until the tire pressure is increased to the nominal pressure.

Each time the ignition is switched off and on again, the hard warning re-appears as a reminder and can be acknowledged again if necessary.